ULN2003 replacement

Discussion in 'General Electronics Chat' started by hurdevan, Feb 22, 2010.

  1. hurdevan

    Thread Starter New Member

    Feb 21, 2010
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    I am trying to build a set of led lights that would scroll left or right for a friend. He bought be the lights and they came with a controller. My first attempt failed even though I tested it and it worked fine. The ULN2003's fried and I had even tested the load on them. The whole thing is supposed to be attached on his car.

    There are four sets of lights but each set have a subset of 3 lights and I want each subset to beadle to be turned on individually. Each subsets of LED's runs straight 12 volts. I could not get much information about that lights so I don't know how much current is required by the lights.

    I am able to run one set, 3 subsets, threw the ULN2003 without any trouble; additionally, that is the most that's suppose to go threw the ULN2003 at any single point of time.

    You can see the basic idea of what I am doing in the diagram. The power supply for the Attiny came off of the original controller for the lights. It was a rectifier diode and a resister. I can't give you any information on those because I can't access it right now(Because I rushed and sent the whole project to my friend...Stupid).

    Anyways the UlN2003 fried and I need a replacement that would work for this. Or, what is it that I did wrong? I am a complete NOOB when it comes to this stuff.

    Any suggestion?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    1,728
    Why don't you come back when you can post more information about the power supply, the controller, and the current demands for the lights?

    Because without that kind of information, we're in the dark - and so is your friend.
     
  3. hurdevan

    Thread Starter New Member

    Feb 21, 2010
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    OK see what I can do.

    Actually, on the board where I got the power supply from is labeled 470. And I forgot to mention that there was a 47uf capacitor.

    But as for the lights, all I know is that I could hook them straight to the car battery and they would work. Also, I tested the lights threw the ULN2003 on the car without any difficulties. And its not like anything else fried, just the ULN2003's.
    <snip> are the lights my friend bought.

    Thanks for the quick reply.
     
    Last edited by a moderator: Feb 23, 2010
  4. hurdevan

    Thread Starter New Member

    Feb 21, 2010
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    0
    OK. I changed things a little.
    I got rid of the power supply that I did not really know about.
    The old power supply was a rectifier diode, 470 resister and a 47uF capacitor. But I replaced it with a LM7805.

    You can see what I have in the schematic I made.

    As for the lights, my friend emailed the person he got them from and asked him but what the required amps was on the lights. Some how I don't the reply.

    Here is what he said.
    I do believe that .42 amps is a little small and also well below the ULN's rating. He might mean .42 amps per LED. Ok, there are 3 leds in each little sub section. That would be 126 MAmps. Still well below to the ULN's rating. Each darlington in the ULN rated for 500 MAmps and the most that will be activated is three. So, that makes 378 total on the ULN.

    Yet they still blew.

    I emailed another person who sells that same product and have yet to get a response.
     
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  5. SgtWookie

    Expert

    Jul 17, 2007
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    I don't know about the ATTiny. Most uC's I'm familiar with require a Vcc/Vdd of 5.5v or less, so you might be OK with 5v for the ATtiny supply. Make certain that you have a 0.1uF cap on both the input and output of the 7805. You can add more capacitance if you think you need it, but you need to have the small caps on there to prevent oscillation at high frequencies.

    The ULN2003 actually should only be operated at a maximum of 350mA sink per output, but not all on at once. You also need to ensure adequate heat sinking for the IC. Using nice fat/wide traces on a 2oz copper PCB can help quite a bit to get rid of the heat.
     
  6. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The lights use up to 0.42A each. If each output drives three lights then the current is 1.26A which is much too high for a little ULN2003A to drive.

    If they are incandescent light bulbs then they draw 4.2A each when they are turned on.
     
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